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21 Days in a Weightless Bed Can Affect the Body Like a Trip to Space

An astronaut floats above the Earth.
Credit: NASA/Unsplash
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A study suggests that some changes the body undergoes during a trip to space can also happen after a few weeks of weightlessness on Earth.

The seven astronauts currently on board the International Space Station (ISS) will arrive back on Earth as changed people. Not just because they have seen the awe-inspiring sight of dawn cresting the horizon from 250 miles above the Earth’s surface (or because they have had to drink recycled pee for months), but because being in space physically alters the body.

The NASA Twin study, which examined identical twins Scott and Mark Kelly, provided a fascinating insight into these changes. While Scott spent a year in space, Mark remained on Earth. Scott, on return to Earth, showed differences in his gene expression, telomeres – caps on the ends of our DNA strands that are thought to relate to aging – and was even temporarily two inches taller.

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New research from a Swedish research group shows that some of these changes to the body can happen even without taking a trip to space.

Weightless in a waterbed

The study, led by Lisa Westerberg, principal researcher at the Department of Microbiology, Tumor and Cell Biology at the Karolinska Institutet, analyzed blood samples taken from volunteers who spent 21 days almost entirely confined to dry immersion (DI) beds. These are effectively specialized waterbeds that make the body feel like it is floating.

A summary of the study. Blood samples are taken from volunteers lying in DI beds. T cells are isolated from their blood, and the effects of microgravity on T-cell activation are studied. Credit: Carlos Gallardo-Dodd

Ten volunteers spent almost their entire days in bed, with a short break for essential functions. The team had expected some significant changes to happen to their volunteers based on previous studies. “They get a lot of pain in their back on day two or three and they actually got taller by two to three centimeters,” explains Westerberg. That pain, which is also reported by astronauts on the ISS, is thought to be caused by changes to the bones of the spine. The change in height, as for astronauts, was temporary.

The study’s real novelty was contained in the patients’ blood. No work had previously analyzed data from as many patients exposed to weeks of DI at once. The samples Westerberg and her team analyzed were taken from the volunteers before they began the DI protocol, and then each week for four weeks after.

The team analyzed the gene expression data produced by white blood cells called T cells. “Day 7 and 14 is where we saw the greatest differences in the gene expression profiles,” says Carlos Gallardo-Dodd, a PhD student at Karolinska Institutet and co-first author of the paper. The team saw that genes linked to an immune process called activation, where T cells become primed to take on threats to the body, were suppressed over the first two weeks of DI. This chimes in with previous studies that have shown that astronauts on mission are more likely to get sick and are more vulnerable to dormant viruses, such as chickenpox. “This finding,” says Gallardo-Dodd, “could help explain the impaired immune response that astronauts have in space.”

Reversed and remodeled

Interestingly, many of these genes changes the DI volunteers experienced reversed by day 21. “This is what we termed remodeling or adaptation of T cells,” says Gallardo-Dodd. “This was quite puzzling to us,” he adds. The team aren’t sure how this remodeling might occur. They also noted that some markers again dropped significantly in the last time point measured – a week after the volunteers left DI. This finding matches up with findings from the NASA Twin study, where Scott Kelly’s blood samples continued to show immunological changes after his return from space.

Westerberg and Gallardo-Dodd acknowledge that the study has some drawbacks. Two of the volunteers’ blood could not be analyzed due to contamination, leaving a small sample size of eight volunteers. Furthermore, the DI work was originally conducted in the Russian Academy of Sciences/Physiology, a center for space research, in 2018. Not only was there only a small volume of samples left for the Swedish team to analyze, which limited the depth of the research the team was able to complete, but the ongoing war in Ukraine has ended the prospect of any future cross-institute collaboration.

Nevertheless, the team hopes to put immune cells to a further test in the near future, by placing them on research rockets that are to be launched from the Esrange Space Center in northern Sweden next year. This will allow the researchers to test more questions about the effect of rocket travel on immune cells.

The question remains: why does weightlessness impair immune function? Westerberg points to studies of skin cells loaded on to the ISS. These showed that space travel remodeled the cellular “skeleton” that supports the skin cells’ structure. The team says similar effects on immune cells might impair their ability to respond to infection. More research will need to go into developing techniques to keep long-term astronauts healthy.

Do so-called space tourists have anything to worry about? “It could be a risk,” says Westerberg, “But I think it’s risky for so many reasons not related to human health!”

Reference: Gallardo-Dodd CJ, Oertlin C, Record J, et al. Exposure of volunteers to microgravity by dry immersion bed over 21 days results in gene expression changes and adaptation of T cells. Science Advances. 2023: 9. doi: 10.1126/sciadv.adg1610